It is common to employ annular apparatus, including an antenna, for electronically transmitting tire or wheel identification or other data at radio frequency. The apparatus includes a radio-frequency transponder comprising an integrated circuit chip having data capacity at least sufficient to retain identification information for the tire or wheel. Other data, such as the inflation pressure of the tire or the temperature of the tire or wheel at the transponder location, can be transmitted by the transponder along with the identification data.
It is known in the art to employ an annular antenna to transmit, at radio frequencies, data from a transponder contained within the structure of a tire or tire and wheel assembly. The antenna comprises a wire or strands of wire formed into a loop that may be sheathed in an extruded covering formed from a suitable material such as plastic. The plastic sheath in combination with the antenna form a unitary body that may be affixed to a green tire in a pre-build assembly process or attached to a finished tire in a post-cure operation. While the antenna and transponder may be incorporated into a tire during “pre-cure” manufacture, in practice it is very difficult to do this. Both radial ply and bias ply tires undergo a substantial diametric enlargement during the course of manufacture. Bias ply tires are expanded diametrically when inserted into a curing press, which typically has a bladder that forces the green tire into the toroidal shape of the mold enclosing it. Radial ply tires undergo diametric expansion during the tire building or shaping process and a further diametric expansion during the course of curing. Any annular antenna and the electronic circuitry associated therewith built into the tire must be able to maintain structural integrity and the mechanical connection between the antenna and transponder package during the diametric enlargement of the tire during its manufacture. Once assembled into the tire, any detected malfunction in the antenna, transponder, or antenna to transponder connection that cannot be repaired destroys the utility of the tire and may necessitate a scrapping of the tire. Hence, placement of an annular antenna-transponder assembly into a tire during its manufacture carries risk that subsequent failure or breakage of assembly components will necessitate the destruction of the otherwise suitable host tire.
Not only is the risk of damage to an annular antenna-transponder system present during its incorporation into a tire during manufacture, but damage to such systems are not uncommon from operation of the tire on a vehicle. Loop antennas and the electronics associated therewith are subjected to substantial compressive strain and at the sidewall a high strain amplitude. Such locations represent high load and deformation to regions of the tire. Consequently, antenna, transponders, and the connections therebetween in such locations are prone to breakage and mechanical or electrical failure.
In order to protect the electronics from undergoing the rigors of a tire cure cycle, it has been proposed that the annular antenna apparatus be applied to a tire in a post-cure operation. The antenna assembly is formed by extruding rubber over an antenna into a specific shape, typically annular, and then the antenna assembly is cured. The antenna, in the cured composite, may then be threaded through an electronic package. Finally, the rubber composite and electronics package is over cured with rubber. The annular antenna assembly may then be glued as a finished unit to the inner side wall of a tire.
While working well, several shortcomings prevent such an antenna assembly and assembly procedure from representing an ideal solution to the needs of the industry. First, sheathing the antenna wire(s) within an elastic sheath, while protecting the antenna, may not allow sufficient freedom of movement in the antenna loop. Such restriction against antenna elongation can cause antenna breakage over time. Secondly, the steps of attaching the electronics package to the antenna wire(s) and over molding the electronics package in a secondary step adds complexity and labor to the antenna apparatus assembly procedure, increasing assembly time and undesirably adding to the cost of the resultant tire.
There is, accordingly, a continuing need for an antenna apparatus and attachment procedure for easily and efficiently incorporating the assembly into a tire. Such a procedure preferably applies the antenna assembly to an electronics package in a post-cure procedure in order to protect the electronics from the rigors of a tire curing cycle. The antenna apparatus must provide sufficient structural integrity to withstand the stresses attendant use in a vehicle-mounted tire and protect the structural integrity of the antenna in such an environment. Moreover, the antenna apparatus ideally will maintain the antenna in its optimal, intended configuration and shape during the tire's life. Since the performance of the tire pressure monitoring system is dependent upon effective communication between the tire electronics and a remote reader via the antenna, maintaining the antenna in an optimal configuration is highly desirable. Additionally, the desired antenna assembly and method of assembly will provide a means for interconnecting the antenna cable an electronics package in a post-cure procedure that is both cost effective and reliable.